Extramedullary hemopoiesis is the result of a compensatory mechanism against many chronic hematological diseases that are characterized by bone marrow depression. These conditions include thalassemia major or intermedia, sickle cell disease, polycythemia vera, chronic myelogenous leukemia, and hereditary spherocytosis. The most common sites of occurrence are the liver, spleen, and lymph nodes,1but many tissues have the potential to exhibit extramedullary hemopoiesis, such as the kidney, adrenal glands, breasts, spinal cord, pleura, endometrium, intracranial cavity, and intrathoracic cavity. Intrathoracic extramedullary hemopoiesis is rarely seen and is usually asymptomatic, requiring no therapy.2However, it may sometimes present with spinal cord compression, pleural effusion, massive hemothorax, or dyspnea.3It is important to distinguish a mass caused by extramedullary hemopoiesis from other lesions involving the posterior mediastinum. Diagnosis is based on clinical and radiological findings, with magnetic resonance imaging as the diagnostic modality of choice.4The differential diagnosis includes neurogenic tumors, lymphomas, primary and secondary malignant lesions, extrapleural cysts, and paravertebral abscesses. Biopsy may sometimes be necessary to confirm the diagnosis,2and surgery and radiotherapy may be needed to treat symptomatic patients with spinal cord compression.